Conventional heat sealing arrangements employ a heated bar or plate that is brought into contact with the back of a flexible material which is sealed to a semi-rigid material. Since the sealer is rigid, it cannot compensate for irregularities in either material being sealed.
Another known heat sealing arrangement utilizes a fluid heated heat sealing member which includes a body of material of low thermal conductivity and a strip of material of high thermal conductivity in communication with a heat exchange fluid passage formed in the body of low thermal conductivity. In this known arrangement non-yieldable pressure applying elements are utilized which are not well adapted for applying uniform sealing pressure and temperature to irregular areas to be sealed. U.S. Pat. No. 4,062,718 is representative of this known arrangement.
Another known device for sealing covers to containers utilizes a non-yieldable element arranged to apply heat and pressure to the lid of a container thereby to seal the lid to the container flange and is arranged to cooperate with a yieldable beveled compressible member against which the container flange rests. In this arrangement the sealing pressure and temperature may not be applied uniformly throughout the sealing area due in part at least to the beveled or inclined disposition of the sealing surface of the yieldable compressor element. Canadian Pat. No. 957,662 is representative of this known device.
Still another arrangement for sealing containers utilizes a heated sealing head having a groove over which a flexible membrane is secured and in which heated liquid is disposed. Thus the flexible membrane together with the heated liquid forms a readily adaptable structure which conforms to any surface irregularities and to a degree of misalignment between the sealing head and the open end of the flanged cup-shaped container to be sealed. U.S. patent application Ser. No. 929,512 filed July 31, 1978 and assigned to the assignee of this invention is representative of such apparatus.